The spinocerebellar ataxias (SCAs) are a genetically heterogeneous group of dominantly inherited progressive ataxia disorders. More than 30 different gene loci have been identified so far. The most common SCAs, which together account for more than half of all affected families, are SCA1, SCA2, SCA3, and SCA6. Each of these disorders is caused by a translated CAG repeat expansion mutation. SCA1, SCA2, and SCA3 usually have an onset between 30 and 40, and SCA6 usually begins at the age of 50 to 60. In addition to progressive ataxia, SCA1, SCA2, and SCA3 frequently present with additional non-ataxic symptoms, including parkinsonism. Carbidopa/levodopa was found to have a good therapeutic effect on parkinsonism.